docs: def ratechangebase(self, ratefactor, current_base, new_base):
          """
          Local helper function for changing currency base, returns new rate in new base
          Defaults to ROUND_HALF_EVEN
          """
          if self._multiplier is None:
              self.log(logging.WARNING, "CurrencyHandler: changing base ourselves")
              # Check the current base is 1
              if Decimal(1) != self.get_ratefactor(current_base, current_base):
                  raise RuntimeError("CurrencyHandler: current baserate: %s not 1" % current_base)
              self._multiplier = Decimal(1) / self.get_ratefactor(current_base, new_base)
          return (ratefactor * self._multiplier).quantize(Decimal(".0001"))